While many of the types of heating in the drop down list on search screens or in Add/Edit are self explanatory (baseboard, hot air, hot water, etc.), there are a few options that are somewhat uncommon or unfamiliar.
Baseboard is the heater's location along the bottom of the wall. The idea behind this location is that heat naturally rises so, by starting out along the floor, the heat slowly rises into the area between the floor and ceiling where you spend most of your time.
Gas on gas is a combination stove/oven and heater, both of which run on natural gas. They can be run independently or at the same time. The heater portion of the appliance is used to heat the room, while the stove/oven is used for meal preparation.
Heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using the refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing heat from the enclosed space and rejecting it outside. Units that only provide cooling are referred to as air conditioners.
Hot air is a way a cooling or heating system distributes air throughout a home or a structure. The air is pushed through ducts and vents that are connected to a unit that heats or cools. This is in opposition to a central air system. The unit is almost always located outdoors and still uses ducts and vents.
Gravity warm air is an older type of heating system (usually found in homes built in the late 1800s through mid 1900s) where there are ducts but no fan to circulate the warm air. Instead, the gravity heat system allows warm air to naturally rise into the home through floor vents.
Hot water is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating.
Hydro Air is a combination of a hot water and a hot air system. Water is boiled and sent through pipes to a coil in an air handling unit. A blower then passes air over the hot coil, creating hot air which is then distributed throughout the house through a vent system.
Radiant is the effect you feel from the warmth of a hot stovetop element from across the room. When radiant heating is located in the floor, it is often called radiant floor heating or simply floor heating.
Radiator is a heat exchanger used to transfer thermal energy from one medium to another for the purpose of cooling and heating.
Solar is space heating by capture and conversion of radiant energy from the sun (use of sunlight to heat water or air). There art two types of Solar heating for buildings: passive and active.
Space heater is a self-contained appliance, usually electric, for heating an enclosed room.
Steam is a system of heating (as for a building) in which steam generated in a boiler is piped to radiators in the various parts of the system with the condensed steam being returned to the boiler for recirculation.
Wall unit is a heating unit that is installed in or attached directly to a wall.
Wood/coal stoves are appliances such as fireplace stoves, room heater/fireplace stove combinations, cookstoves and ranges, and radiant and circulating heaters.
Zoned is a heating and cooling system that uses dampers in the ductwork to regulate and redirect air to specific areas of the home. This allows for the creation of customized temperature zones throughout the home for increased comfort and efficiency.